Dawn of war. If you want try campaing, try first and expansion, winter assault. But be warned: game is pretty dated. But for mechanics, go for soulstorm and jump into skirmish. You will be shocked from variety of races that game has. And they are not copy's of each others, every single one plays very differently from another.
Original dawn of war 2 campaing is more grind feast. I wouldn't recomend it for trying. Go for expansion- chaos rising. It has a most solid campaing, but for multiplayer, you must buy another expansion- retribution. Single player and multi player is completely different games! And I would strongly reccomend to try it, but be warned: multi player is extremely unforgiving to new players. In this game, even much more expensive units, can be easely beaten by foes, who they supposed to counter in the first place!